Estimating Landward Migration of Nearshore Constructed Sand Mounds

Abstract

A model for the migration of submerged mounds constructed offshore of the day-to-day surf zone but within the depths disturbed by waves during storm events is developed. The model considers net shoreward sand transport due to the velocity asymmetry of finite-amplitude waves, and is based on Bagnold's bed-load–sand transport equation with Stokes' second-order wave theory. Conservation of sand considerations lead to an equation that indicates mounds will behave according to a nonlinear convection-diffusion model. The “convection coefficient”–like parameter, which is based on the wave and sand-transport models only, is proposed as an estimate of the migration rate for submerged mounds. The expected value of mound movement in different depths can be estimated with site-specific wave-climate data. The full sediment-transport equations successfully simulate the migration of a mound at Silver Strand State Park, California, in 1989. The expected value of the mound-movement parameter gives results that agree reasonably well with measured migration rates both at Silver Strand and offshore of Mobile, Alabama.